Studies in animals are being carried out to determine the in vivo activity of a new class of antimicrobial peptides isolated from the skin of the African frog Xenopus laevis and called magainins. This family of peptides consists of two closely related peptides that are each 23 amino acids which inhibit growth of numerous species of bacteria and fungi in vitro. An animal model of experimental bacterial keratitis induced in adult New Zealand white rabbits was used to determine the in vivo relevance of the antimicrobial activity of magainins. Pseudomonas aeruginosa corneal infection was primarily considered because it is the most destructive and the most difficult to treat corneal infection in humans. Each cornea was infected by an intrastromal injection of 100 bacteria. The topical treatment with magainin drops or ocular ointment was started either 4 hours or 20 hours after the infection. The control animals were either not treated or treated with the vehicle (PBS or petrolatum plus mineral oil). These preliminary studies demonstrated the in vivo activity of the magainin by showing a less severe corneal abscess in the treated animals with a delayed onset of the abscess as compared to the control animals. Although the animals could tolerate well the treatment, magainin drops and ointment induced a chemosis with a conjunctival hyperhemia by themselves which can aggravate the conjunctival inflammation related to the infection.